The investigation on the absorption and metabolism of labeled nicotinic acid, nicotinamide, pyridoxine, pyridoxamine, pyridoxal phosphate and pyridoxamine phosphate by perfused rat intestine will be continued. Comparisons will be made between luminal and vascular administration. Kinetic studies will be used to ascertain the reaction sequences by which each metabolite arises. Whole animal experiments will be done to validate the conclusions where possible. Follow-up studies of the enzymology of the pathways suggested by the perfusion studies is anticipated.